1. Field of the Invention
The present invention relates to a copying machine having two developing devices for color printing.
2. Description of the Prior Art
Copying machines have included two developing devices of different colors wherein monochrome color copying such as red color copying or yellow color copying can be carried out by selecting either one of the developing devices through operation of a key board on the copying machine.
Another copying machine has employed simultaneous color copying or one scan, two color copying by switching and using a plurality of developing devices in one exposure operation for printing a polychrome picture on one sheet of copying paper. According to the simultaneous color copying of such a copying machine, it is possible to print different colors on the left half portion and the right half portion of a picture and it is also possible to print a part of the picture with a different color in order to emphasize that part. One advantage of the proposed simultaneous color copying is that since the simultaneous color copying can be carried out in one copying operation, the step of setting the original document on the document platform and the step of operating the copying machine need only be performed once and thus, the copying time can be decreased.
One problem associated with the aforementioned simultaneous color copying machine is that if two developing devices of the same color are selected, the color pictures are printed twice with the same color. Accordingly, a needless developing operation if performed and the developing devices are unnecessarily worn.